1. Field of the Invention
This invention broadly relates to a cassette for measuring one or more parameters of blood, and is especially suitable for use during surgical procedures.
2. Description of the Related Art
Various characteristics or parameters of blood are often monitored in real time during certain surgical procedures. For example, during open heart surgery the surgeon and other members of the surgical team often monitor the pH of the patient's blood as well as the concentration of certain blood gases such as carbon dioxide and oxygen. In many instances, the parameters of the patient's blood are monitored not only as the surgery is progressing, but also in the time period before and after the surgical procedure.
Measurement of blood parameters is often accomplished using an extracorporeal blood circuit having lengths of flexible tubing with passageways that are in fluid communication with the vascular system of the patient. In many extracorporeal blood circuits, one or more sensors that are useful for determining blood parameters are placed adjacent the passageway and are connected to a processing unit. The processing unit is typically connected to a display device such as a monitor so that the surgical team can review the parameters of interest when desired. Optionally, the processing unit is connected to a recording device such as a printer to provide a log of the parameters over a period of time.
Optical sensors are often used for sensing blood parameters in real time. For example, U.S. Pat. No. Re. 31,879 to Lubbers et al. and U.S. Pat. No. 5,403,746 to Bentsen et al. describe fluorescent sensors that respond to light in accordance to the partial pressure of oxygen, the partial pressure of carbon dioxide and the pH of blood. Sensors that function on the principles of light absorbance are described, for example, in U.S. Pat. No. 4,041,932 to Fostick.
Extracorporeal blood circuits having sensors for determining blood parameters may be arranged in various manners, and the manner selected for use in a particular instance often depends upon the preferences of the surgical team. In some cases, the sensors are mounted in a housing located along a length of relatively small-diameter tubing that is connected at only one end to the patient's blood supply, and a device such as a syringe is used to draw a sample of blood past the sensors. Examples of such circuits are described in U.S. Pat. No. 4,989,606 to Gehrich et al. Such circuits are an advantage in that the length of tubing connected to the sensors can be coupled to the blood supply at any convenient time before or during the surgical procedure, but are a disadvantage in that the blood does not continuously circulate in the length of tubing connected to the sensors and as a result the accuracy of the sensed parameter may be adversely affected.
Another type of extracorporeal blood circuit has sensors located along tubing that is part of an arterial or a venous passageway connected to an oxygenator. The sensors in this type of circuit are often connected to an element known as a flow-through cell that has fitting on opposite sides for coupling to the circuit tubing. Flow-through cells are described, for example, in U.S. Pat. No. 4,640,820 to Cooper. Flow-through cells are often favored because a fresh supply of blood is continuously circulated past the sensors. Unfortunately, flow-through cells are in series relation to the circuit tubing and hence cannot be installed after blood has begun to flow through the tubing.
Optical sensors for measuring blood parameters are often optically coupled to a remote measuring device that includes a source of light for directing light to the sensors as well as apparatus for analyzing the light returned from the sensors. In many systems, a bundle of optical fibers extends from the remote device to a transmission block or retainer, and a releasable coupling is provided to detachably connect the retainer or block to the cell or housing that supports the sensors. For example, U.S. Pat. No. 4,989,606 to Gehrich et al. describes a transmission block that is detachably secured to a housing by a movable securement assembly having a swingable member and a threaded screw for clamping the housing between an outer end of the member and the block.
While many of the components known in the art for measuring blood parameters are satisfactory in certain instances, there is a continuing need to improve the components in order to facilitate ease of use without adversely affecting the accuracy of the measurements or unduly increasing the cost of the components. Moreover, it would be desirable to provide components that can be used in a variety of blood circuit configurations.